Don't use modules

Feel free to revert this if you have a strong feeling about it. But so
far as I can see, it adds a lot of complexity for basically no upsides.

tai64n_test.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"testing"
+	"time"
+)
+
+/* Testing the essential property of the timestamp
+ * as used by WireGuard.
+ */
+func TestMonotonic(t *testing.T) {
+	old := TimestampNow()
+	for i := 0; i < 10000; i++ {
+		time.Sleep(time.Nanosecond)
+		next := TimestampNow()
+		if !next.After(old) {
+			t.Error("TAI64N, not monotonically increasing on nano-second scale")
+		}
+		old = next
+	}
+}